Summary: Adult human erythroblasts arise from hematopoietic stem cells in the peripheral blood of humans in response to erythropoietin. This process is called erythropoiesis. In many erythroid diseases including hemoglobinopathies, anemia and erythroleukemia, the process of erythropoiesis is abnormal or damaged by the underlying pathology. In order to better understand the molecular mechanisms responsible for these diseases, ex vivo model systems of erythropoiesis were developed using hematopoietic stem cells collected from the peripheral blood of humans. In this study, cells are harvested from peripheral blood and used for ex-vivo assays of erythropoiesis. In addition, collaborative efforts with the department of transfusion medicine are aimed toward improved methods for the collection of hematopoietic stem cells, and specialized methods are being developed for patients with erythroid diseases.